Phrynosoma ditmarsi, the rock horned lizard, lives in northern Mexico at rocky sites in oak and oak-pine woodlands and short-tree Sinaloan deciduous forest along the western aspect of the Sierra Madre Occidental in the state of Sonora, north of Yecora, at elevations of 1050-1425 meters. This species was 'lost to science' for 65 years: it was initially described at the end of the 19th century, but its limited distribution combined with an imprecise holotype locality record made it difficult to re-locate. Click here to read the story of its rediscovery. Phrynosoma ditmarsi can be distinguished from other horned lizard species by the following: occipital and temporal horns reduced to flaring expansions; deep and narrow occipital notch; high post-orbital ridge; large vertical expansion of the mandibles; bare tympanum in the anterior neck fold posterior to a vertical row of four spines; and one row of lateral abdominal fringe scales surrounded by prominent scales.

About the Species

This specimen (WLH 1133) was collected by Dr. Wendy Hodges on the steep hillsides 13 miles east of Baviacora, Rancho la Palma, Sonora, Mexico. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Hodges of the Department of Biology, University of California, Riverside. Funding for scanning was provided by a National Science Foundation grant (DBI-0204459) to Dr. Hodges. Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of the Department of Geological Sciences, The University of Texas at Austin.